1. Field of the Invention
The present invention relates to a reversible thermosensitive recording material capable of recording and erasing images repeatedly by utilizing its property that the transparency can be changed reversibly from a transparent state to an opaque state, and vice versa, depending upon the temperature thereof. The present invention also relates to an image display method using this reversible thermosensitive recording material.
2. Discussion of Background
As a reversible thermosensitive recording material which is capable of recording images and erasing the same repeatedly, a recording material provided with a thermosensitive recording layer comprising a resin such a polyvinyl chloride resin and an organic low-molecular material such as a higher fatty acid which is dispersed in the resin is disclosed, for instance, in Japanese Laid-Open Patent Application 55-154198. In order to prevent the deformation of the surface of such a recording material or to avoid a decrease in transparency of the recording material by the heat or pressure applied by a heat application means for image formation such as a thermal head, reversible thermo-sensitive recording materials provided with a protective layer comprising a heat resistant resin such as ultraviolet curing resin or electron-radiation curing resin are disclosed in Japanese Laid-Open Patent Applications 1-133781 and 2-566.
In the reversible thermosensitive recording materials provided with the protective layer comprising the above-mentioned heat resistant resin, the deformation of the surface thereof is small. However, when recording and erasing steps are repeated by use of a thermal head, in particular, on an identical portion of the recording material, the surface of the recording material is scratched by the thermal head, and part of the protective layer is peeled off the recording layer and adheres to the thermal head. When the peeled protective layer portion adheres to the thermal head and is built up thereon, or when some dust adheres to the surface of the thermosensitive recording material and such dust is built up between the thermal head and thermosensitive recording material with time, heat transfer from the thermal head to the recording material is hindered and eventually normal image formation becomes impossible, or image formation cannot be carried out in the portions where such dust is built up.
Furthermore, in order to prevent the sticking between the thermal head and the reversible thermosensitive recording material, reversible thermosensitive recording materials provided with a protective layer comprising as the main component a silicone rubber, a silicone resin, or a polysiloxane graft polymer are proposed, for instance, in Japanese Laid-Open Patent Applications 63-221087 and 63-317385. These recording materials, however, also have the problems that when images are formed repeatedly on an identical portion by a thermal head, the surface of each recording material is scratched because of the insufficiency of the hardness thereof or because the protective layer is peeled off the recording layer. As a result, image formation becomes impossible.